The present invention relates generally to determining thermal turn on energy (TTOE), more particularly for fluid ejection devices.
Inkjet printing is a non-impact printing process in which droplets of ink are deposited on print media, such as paper, transparency film, label stock, textile and other materials. Inkjet printing involves the ejection of fine droplets of ink onto the print media in response to electrical signals generated by a microprocessor.
There are two basic means currently available for achieving ink droplet ejection in inkjet printing: thermally and piezoelectrically. In thermal inkjet printing, electrical resistance heating is used to vaporize the ink, which produces a bubble which acts as a piston to expel ink through an orifice in the inkjet printhead toward the print medium. Printheads of this type are provided with a plurality of orifices, each orifice being associated with an electrical heating resistor which, when electrically energized, vaporizes and ejects ink droplets from an ink chamber associated with the orifice and resistor. A microprocessor selects the appropriate resistors to be fired and directs an electrical current thereto to achieve resistive heating and consequential ejection of ink vaporized by the heating through the orifice associated with the selected resistor.
A thermal inkjet printer requires a certain minimum energy to fire ink drops of the proper weight and volume, herein called TTOE. TTOE differs for different printhead designs and varies among different samples of a single printhead design as the result of manufacturing tolerances and among resistors within a printhead. As a result, thermal ink jet printers are operated at a fixed ink firing energy that is greater than the expected TTOE for the printhead cartridges it can accommodate. The TTOE test is a test run in the printer to determine the average operating energy for a given printhead so that manufacturing variations can be dealt with on a printhead by printhead and printer by printer basis.
It is accordingly desired to provide a TTOE test in which the number of ink droplets required for the test is reduced with resultant reduction in the generation of objectionable aerosol and wasted ink.
In one embodiment of the present invention, a method of determining thermal turn on energy comprises heating a fluid ejection device to a predetermined temperature that is below a fluid ejection temperature; applying firing pulse bursts to a resistor of said fluid ejection device, the pulses in each of said bursts having a predetermined reference pulse energy and a predetermined pulse frequency to eject a predetermined count of fluid droplets; and incrementally varying the drop count from said predetermined count while sampling the temperature of the fluid ejection device after said pulse bursts are applied.
Many of the attendant features of this invention will be more readily appreciated as the same becomes better understood by reference to the following detailed description and considered in connection with the accompanying drawings in which like reference symbols designate like parts throughout.